1. Field of the Invention
The present invention relates to a transparent substrate with a multilayer antireflection film having electrical conductivity, achieving high transmittance.
2. Description of Related Art
Heretofore, there have been known transparent substrates such as glass plates coated with a transparent electrically conductive film such as indium tin oxide (ITO), SnO2, or the like. These would be used for electrodes of photoelectric sensing elements such as a solar cell and electrodes of liquid crystal and other display devices or touch panels. In particular, the substrate to be used in the touch panels or the liquid crystal displays needs to have high transmittance with respect to the light of a visible wavelength region and optimum resistance. For manufacture of liquid crystal displays, furthermore, a transparent electrically conductive film having a low resistance of 100xcexa9/xe2x96xa1 (ohm per square) or less, more preferably, 50xcexa9/xe2x96xa1 or less is desired to allow sharp display of moving images.
For small-sized liquid crystal displays for use in cellular phones and the like, instead of the glass substrate, a plastic substrate is being put to use with a high frequency and with a multilayer film formed thereon. This is because the plastic substrate is lighter and less fragile than the glass substrate.
To form the transparent electrically conductive film with a lower resistance value, in general, the film thickness of the conductive film has to be more increased. However, as the thickness of the conductive film increases, the transmittance still further lowers, which makes it difficult to achieve high transmittance.
When the same film as the multilayer film formed on the glass substrate is formed on the plastic substrate, the resistance value of the electrically conductive film becomes higher and the transmittance becomes lower as compared with in the glass substrate. This results from that the transmittance of plastic itself is lower than that of glass and also that the film formation on the plastic substrate can not be executed under a high temperature (about 300xc2x0 C.) such as used in the film formation on the glass substrate to prevent melting of the plastic substrate.
The present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide a transparent substrate with a multilayer antireflection film having electrical conductivity, the film being capable of achieving high transmittance while having low resistance even if a plastic substrate is used.
Additional objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the purpose of the invention, there is provided a transparent substrate with a multilayer antireflection film having electrical conductivity, the film including a transparent dielectric thin-film and a transparent conductive thin-film layered on the transparent substrate, wherein the transparent dielectric thin-film consists of a first thin-film layer having a lower refractive index than a refractive index of the transparent substrate and a second thin-film layer having a higher refractive index than the refractive index of the first thin-layer, and the transparent conductive thin-film consists of a third thin-film layer, the first, second, and third thin-film layers being formed on the transparent substrate in this order from the transparent substrate side so that the third thin-film layer is an outermost layer, and an optical thickness of the third thin-film layer is determined to provide a desired surface resistance value, and optical thickness of the second thin-film layer is determined so that the sum total of the optical thickness of the second thin-film layer and the optical thickness of the third thin-film layer is approximate xcex/2.
In another embodiment of the invention, there is provided a transparent substrate with a multilayer antireflection film having electrical conductivity, the film including a transparent dielectric thin-film and a transparent conductive thin-film layered on the transparent substrate, wherein the transparent dielectric thin-film consists of a first thin-film layer having a lower refractive index than a refractive index of the transparent substrate and a second thin-film layer having a higher refractive index than the refractive index of the first thin-layer, and the transparent conductive thin-film consists of a third thin-film layer having a higher refractive index than the refractive index of the transparent substrate, the first, second, and third thin-film layers being formed on the transparent substrate in this order from the transparent substrate side so that the third thin-film layer is an outermost layer, and an optical thickness of the third thin-film layer is determined to provide a desired surface resistance value, and optical thickness of the second thin-film layer is determined so that the sum total of the optical thickness of the second thin-film layer and the optical thickness of the third thin-film layer is approximate xcex/2.